title: A single point mutation reveals gating of the human ClC-5 Cl-/H+ antiporter.
abstract: ClC-5 is a 2Cl(-)/1H(+) antiporter highly expressed in endosomes of proximal tubule cells. It is essential for endocytosis and mutations in ClC-5 cause Dent's disease, potentially leading to renal failure. However, the physiological role of ClC-5 is still unclear. One of the main issues is whether the strong rectification of ClC-5 currents observed in heterologous systems, with currents elicited only at positive voltages, is preserved in vivo and what is the origin of this rectification. In this work we identified a ClC-5 mutation, D76H, which, besides the typical outward currents of the wild-type (WT), shows inward tail currents at negative potentials that allow the estimation of the reversal of ClC-5 currents for the first time. A detailed analysis of the dependence of these inward tail currents on internal and external pH and [Cl(-)] shows that they are generated by a coupled transport of Cl(-) and H(+) with a 2 : 1 stoichiometry. From this result we conclude that the inward tail currents are caused by a gating mechanism that regulates ClC-5 transport activity and not by a major alteration of the transport mechanism itself. This implies that the strong rectification of the currents of WT ClC-5 is at least in part caused by a gating mechanism that activates the transporter at positive potentials. These results elucidate the biophysical properties of ClC-5 and contribute to the understanding of its physiological role.
authors.affiliation: G. Zifarelli: Istituto di Biofisica, CNR, Via De Marini 6, I-16149 Genova, Italy. zifarelli@ge.ibf.cnr.it.
authors.forename: Silvia
authors.initials: S
authors.lastname: De Stefano
authors.forename: Michael
authors.initials: M
authors.lastname: Pusch
authors.forename: Giovanni
authors.initials: G
authors.lastname: Zifarelli
mesh_terms: D000818:Animals; D018118:Chloride Channels / Q000502:physiology*; D005260:Female; D006801:Humans; D015640:Ion Channel Gating; D009865:Oocytes; D017354:Point Mutation; D014982:Xenopus laevis
chemical_list: C097503:CLC-5 chloride channel; D018118:Chloride Channels